For example, a photomask (reticle) for use in the semiconductor device microfabrication technology is manufactured by patterning a light-shielding film in the form of a thin film, formed on a transparent substrate, into a transfer pattern. The patterning of the light-shielding film is performed, for example, by dry etching using a resist pattern as a mask. The resist pattern is formed, for example, by the electron beam lithography or the like.
In recent years, in the mask manufacturing field, it has been studied to set the acceleration voltage of an electron beam used in the electron beam lithography to 50 keV or more. This is because it is necessary to reduce forward scattering of an electron beam passing through an electron beam resist and thus to raise the convergence of the electron beam, thereby resolving a finer resist pattern. If the acceleration voltage of the electron beam is low, the forward scattering occurs at the resist surface or in the resist and, when the forward scattering is present, the resolution of the resist is degraded. However, if the acceleration voltage of the electron beam is set to 50 keV or more, the forward scattering decreases in inverse proportion to the acceleration voltage so that the energy applied to the resist due to the forward scattering decreases. Therefore, for example, with an electron beam resist that is used when the acceleration voltage is 10 to 20 keV or the like, the sensitivity of the resist is insufficient and thus the throughput drops. Therefore, also in the mask manufacturing field, it has become necessary to use a chemically amplified resist film as has been used in the semiconductor wafer microfabrication technology. The chemically amplified resist film is highly sensitive to a high acceleration voltage and has a high resolution.
Herein, it is known that when a chemically amplified resist film is used in the mask manufacturing field, for example, in the state where the film density near the surface of a light-shielding film being an underlying film thereof is relatively sparse or rough, there may arise a problem of deactivation of the chemically amplified resist film. Specifically, there is a case where acid catalysis reactions during patterning are prevented at the interface between the light-shielding film being the underlying film and the chemically amplified resist film, so that the resolution is degraded at the bottom of a resist pattern. In this case, there occurs shape failure such as, for example, footing with the positive type chemically amplified resist film or undercutting with the negative type.
This is considered to be caused, for example, by the fact that acid produced in the chemically amplified resist film by exposure is suppressed (quenched) by base components on the chromium oxide surface, the acid diffuses to the light-shielding film side, and so on, so that the sensitivity of the chemically amplified resist film at the interface with the light-shielding film is apparently lowered. In order to solve this problem, a configuration has conventionally been known in which a mask blank is provided with a deactivation suppression film (see, e.g. Patent Document 1). Patent Document 1 discloses a configuration in which an inorganic film of a silicide-based material, an organic BARC, or the like is introduced as an intermediate layer (deactivation suppression film).
Patent Document 1: JP-A-2003-107675